Add types in package.json

[devrnt]

Changes

• Add types entries in package.json

References

• publint was used to detect errors/warnings
• Read more about the "best practices" for a package.json file

There is still room for improvement (having separate declaration files for both CJS and ESM) but this requires changes in the build pipeline which I consider out-of-scope for this fix.

Closes #3

[kossnocorp]

Thank you!

[kossnocorp]

Shipped as @date-fns/utc@1.1.1